1921 .] Recently published Ornithological Works. 551 
of India, has been occupying his leisure for many years 
in investigating the problem of flight, not only in birds, 
but also in flying fishes and insects and even pterodactyls ! 
He published in 1914 a volume on the subject, which 
we fear has not attracted the attention it should have ; 
for his work is of a most interesting nature, and he has 
devised a number of exceedingly ingenious instruments 
and, mathematical methods for recording the speed of 
flight. 
The present short paper deals with the problem of soaring 
flight. How does a bird whose body is heavier than the air 
maintain itself at great elevations without perceptible move¬ 
ment of its wings and in a calm atmosphere ? 
In the present paper Dr. Hankin gives a summary of his 
observations during the l#st ten years, and the conclusion 
he reaches is that “ soaring flight is inexplicable in the light 
of existing knowledge/’ He believes that in some way or 
other the energy involved is derived from the sun’s rays, and 
he hopes that a solution may eventually be discovered by ex¬ 
perimental investigation. The introduction by Mr. Handley 
Page deals with the bearing of soaring flight on mechanical 
aviation. 
Hartert on the Palcearctic Birds . 
[Die Vogel der palaarktisclien Fauna. Von Dr. Ernst Hartert. 
Bd. ii. Heft xi.-xii. pp. 1345-1600; Heft xiii.-xiv. pp. i-xxiv & 
1601-1764; Bd. iii. Heft xv. pp. 1765-1892. Berlin (Friedlander), 
1920-1921. 8vo.] 
The numbers of Dr. Hartert’s invaluable work are coming 
out more quickly now, and we have before us two double 
parts, completing the second volume, and the first part of 
the third volume, containing more matter than we can well 
deal with in a short article. 
In parts xi.-xii. the balance of the Ducks, the Stegano- 
podes, Tubinares, Pygopodes, Columbse, Pterocletes, and a 
portion of the Limicolse are dealt with. Parts xiii.-xiv. 
contain the rest of the Waders and the Gulls (Lari). 
ser. xi.— VOL. 111 . 2 o 
